THICKENING PARAMETERS
Natural and synthetic gums have been used as thickeners for foods, coatings, paints, dyes, explosive slurries, oil well fluids and many other applications. Thickeners impart viscosity to sols in which they are incorporated. When shear force through agitation is applied to the sol and there is no change in viscosity, the behavior of the thickener is said to be nonplastic. When the viscosity of the sol in a quiescent state is greater than when a shear force is applied through agitation, the thickener is said to be plastic. The viscosity of the sol will decrease as the shear force applied increases. The viscosity immediately develops again when the magnitude of shear force is decreased. Generally, when the plastic sol is at rest, the molecules arrange themselves into a more or less stable form. In order to break this stable molecular arrangement and cause the sol to yield, the application of a shear force is necessary. The shear force required to cause the plastic sol to yield and flow is termed the gel strength. Once the gel strength of a plastic sol is overcome, the viscosity of the sol decreases as greater shear force is applied.